What about something to catch the handle? I'm having trouble finding something like this on the web, but I'm imagining something similar to a carabiner, padded on the inside, set up facing away from the wall so that when you open the door, the handle latches inside. In order to release it, you'd just have to press down the spring-loaded part of the mechanism and shut your door. A standard carabiner likely wouldn't do the trick, but if you did something that was a little larger, more of a C-shape, with a relatively smaller mouth, I think it'd work.